Recently, laser-beam cutting has been increasingly employed for machining metals, plastics, wood, etc. Generally, laser-beam cutting machines used for this purpose include a laser beam reflector, such as a bend mirror, to control the direction of a laser beam used as the actual cutting tool.
FIG. 7 illustrates the configuration of a known laser beam reflector disclosed in Japanese Patent Publication No. 109023/1984, wherein a mirror retaining surface 60 of a mirror holder 6 is provided with a laser detecting element 61, formed of a thermistor or the like, having a light absorber applied to one surface thereof. The output end of the laser detecting element 61 is connected to an amplifier 63 via a lead wire 62, and the amplifier 63 is connected to a laser drive source 64 including a high-voltage power supply, etc.
Accordingly, a laser beam 1 generated by a laser oscillator is directed properly if a bend mirror 7 is in a normal state, and is irradiated to the laser detecting element 61 if the bend mirror 7 is damaged or disconnected from the holder 6 (i.e., oriented improperly). As a result, a detection signal is output from the laser detecting element 61, and then is amplified by the amplifier 63, and is input. to the laser drive source 64 to stop the oscillation of the laser.
FIGS. 8(a) and 8(b) show another embodiment disclosed in Japanese Patent Disclosure Publication No. 109023/1984, wherein FIG. 8(a) shows a normal status of a laser beam reflector, and FIG. 8(b) shows an abnormal status of the laser beam reflector. The reflecting surface of a reflecting member 65 made of a laser reflecting material, e.g. aluminum, is formed on the mirror retaining surface 60 of the mirror holder 6 at an angle of reflection different from that of the bend mirror 7. If the bend mirror 7 is in a normal state, the laser beam 1 from the laser oscillator is directed properly, as shown in FIG. 8(a). If the bend mirror 7 is disconnected from the mirror holder 6, the laser beam 1 is reflected by the reflecting member 65 and enters the laser detecting element 61, as shown in FIG. 8(b). An operation similar to that of the embodiment shown in FIG. 7 then is performed to stop the oscillation of the laser.
FIG. 9 is a sectional view illustrating the structure of yet another known laser beam reflector, disclosed in Japanese Patent Publication No. 28094/1987, wherein a bend block 2 reflects and introduces a laser beam 1 to a machining head. A housing 80 is secured to the bend block 2 by a screw 81. A cylindrical mirror holder 3 has a step 82 having a front end inside wall abutting the mirror surface side of a bend mirror 7, and an outward flange formed in the outer periphery of the side opposite to the step 82 (e.g., on the rear end side). The mirror holder 3 is positioned in a predetermined location against the housing 80 by a plurality of screws 83, springs 84, and a screw 85 loaded in the flange. A cover 86 is fixed to the rear end of the mirror holder 3 by screws 87. A screw 88 is engaged with and inserted into the cover 86 for pressing a mirror retainer 6 and for securing the bend mirror 7 to the mirror holder 3. An inlet 89 allows coolant to be circulated into the mirror retainer 6, and an outlet 90 allows the coolant to be discharged from the retainer 6. The mirror retainer 6, cover 86, and screw 88 constitute a pressing mechanism 91.
The operation of the above-described laser beam reflector will be described hereinafter. The bend mirror 7 employed must ordinarily be cleaned or replaced when it becomes dirty or chipped. For example, when the bend mirror 7 is to be removed for replacement, cleaning, etc. because its reflectance capability has been reduced due to dirt, etc., the cover 86 is designed to be freed by first extracting the screws 87 from the mirror holder 3, then removing the cover 86 and mirror retainer 6, and finally removing the bend mirror 7 from the rear end aperture of the mirror holder 3. Meanwhile, the cleaned bend mirror 7 or a new bend mirror 7 is reinstalled by bringing the bend mirror 7 into contact with the step 82 in a reverse procedure of the above-described steps and then securing the bend mirror 7 pressed against the mirror holder 3 via the mirror retainer 6 by the screw 88.
The above-described known laser beam reflector is designed to stop the oscillation of the laser if the bend mirror is disconnected from the mirror holder or if the bend mirror is damaged.
However, when the mirror holder retaining the bend mirror is lifted or disconnected from the fixed side of the laser-beam cutting machine, or when the bend mirror is removed from the laser-beam cutting machine together with the mirror holder for the cleaning or changing of the bend mirror, the laser oscillation cannot be stopped if the laser oscillator is oscillating, i.e. if the laser beam is being irradiated into the bend mirror. To prevent an output reduction of the laser-beam cutting machine, the bend mirror is cleaned or replaced often. However, as a result, the known cutting machine may irradiate the operator, equipment, the building, etc., thus potentially creating a safety problem.
Accordingly, an object of the present invention is to overcome the disadvantages of the conventional systems by providing a laser beam reflector achieving a higher level of safety than that provided by the conventional systems, and by providing a laser-beam cutting machine which employs the laser beam reflector.